For a while now I have thought about going digital, but I have a few questions.

If a game I have played on dics, I then buy digitally, do I still need to download the game to play it? or will it just use the file it installed from the disc?

Will my saved games still work if I switched from playing a disc version to digital? I ask this as I remember back on PS3 I played Infamous when it was released (the disc version) then later it was given away free digitally, so went to play it again only to find my game saves from playing the disc version were incompatible. Is this still the case on PS4 games?

I can't answer your questions, but I'll give your thread a bump.

I can't answer either. Out of Sony and Microsoft, at least one of them said this was how it worked. Said you could loan your friend the disc and they could install it but without the disc, they'd have to buy it.

I say install a game, remove the disc, and try to play it. See if you're prompted to buy. Or just wait for me to Google it. I'm at work and I have nothing better to do.

You can't get digital copies of games you bought on disc... unless you actually buy it again on Xbox Live or PSN. 

If you sell the disc and buy the game digitally the system should simply give you digital right to play the installed game. All your saved game will not be affected.

The game most likely check your license agreement when it lauch if your Xbox Live or PSN account have the digital right then you will be able to play. I have never tried it so let us know. 

Ok, so bought Alien dugutal (which I had on disc)

Cant download game with disc version installed. It doesnt make the version installed bootable without the disc.

So you have to delete the disc version from the HDD, then redownload. Will then see if saves work with game still